1. Field of the Invention
The present invention relates to a baffle plate of a dry etching apparatus for manufacturing semiconductor devices, and more particularly, a baffle plate for minimizing the vacuum level fluctuations in a process chamber, as well as minimizing the accumulation of particles that are generated as by-products of the semiconductor device fabrication process.
2. Description of the Related Art
Generally, semiconductor devices are manufactured by forming multiple layers on a semiconductor substrate wafer, and forming circuit patterns thereon according to the desired electrical properties of a specified semiconductor device.
The patterns on the semiconductor substrate are typically formed by selectively removing portions of the layers on the semiconductor substrate using an etching process.
Conventional etching processes are categorized as wet etching (using chemicals), dry etching (using plasma), and reactive ion etching, which is a type of dry etching with improved plasma efficiency.
A conventional reactive ion etching apparatus is shown in FIG. 1, and includes an upper electrode 12 and a lower electrode 14, to which high frequency power is applied for forming the plasma inside a process chamber 10. When power is applied to the lower electrode 14 the upper electrode 12 functions as ground. The lower electrode 14 is located under the chuck for mounting the wafer W. A transfer apparatus 28 transports the wafers to and from the chuck.
A magnetic coil 15 surrounds the process chamber 10 in order to generate a magnetic field during the etching process. A gas supply line 16 is provided on the upper electrode 12 for supplying, to the process chamber 10, a reaction gas and other gases required for the etching process.
A vacuum chamber 24 is disposed under the process chamber 10, with the vacuum chamber 24 being connected to a vacuum pump 18 for forming the vacuum in the process chamber 10. Valves 20 and 22 are connected between the vacuum chamber 24 and the vacuum pump 18. Gate valve 20 is selectively opened/closed in conjunction with the operation of the vacuum pump 18. Vacuum control valve 22 controls the degree or level of the vacuum in the vacuum chamber 24. This is accomplished by controlling the opening angle of the vacuum control valve 22.
A vacuum indicator 26 is connected to the vacuum chamber 24 for readily displaying the degree of vacuum in the vacuum chamber 24. The vacuum indicator 26 senses the degree of vacuum in the vacuum chamber 24, and inputs it to a controlling part (not shown). Accordingly, the controlling part controls the opening/closing of the vacuum control valve 22, which in turn controls the degree of vacuum in the vacuum chamber 24.
In this embodiment, the degree of vacuum in the process chamber 10 should basically be the same as the degree of vacuum in the vacuum chamber 24, which can easily be ascertained by the vacuum indicator 26 display.
A baffle plate 30 is disposed between the process chamber 10 and the vacuum chamber 24, and has slits for discharging the non-reacting gases and polymer by-products remaining inside the process chamber 10 to the vacuum chamber 24. The baffle plate 30 essentially surrounds the chuck of the lower electrode 14, such that the inner circumference of the baffle plate 30 confronts the outer circumference of the chuck. To effect a wafer transfer, the chuck would descend from this engaged position, move toward the transfer apparatus 28, and thereafter the wafer is mounted on the chuck. The chuck then moves back toward the baffle plate 30 and then rises to the engaged position confronting the baffle plate 30.
As shown in FIG. 2 the baffle plate 30 comprises a plurality of slits 34 formed radially in the annular ring portion 32 of the baffle plate 30 and spaced a certain distance from each other. In the conventional baffle plate, 360 slits are provided.
As shown in FIG. 3 the slit 34 has three distinct sections. The upper 40 part of the slit 34 has an inclined surface, with the widest portion facing the process chamber 10 and thereafter converging as it approaches the middle part. The middle part is vertically formed with a constant width. The lower part facing the vacuum chamber 24 is also vertically formed, but with a constant width greater than that of the middle part.
As described above, the non-reacting gases and polymer 36 by-products remaining inside the process chamber 10 are discharged into the vacuum chamber 24 through the slits 34 of the baffle plate 30. However, as shown in FIG. 3, not all the polymer by-products are discharged to the vacuum chamber 24, and a certain amount of polymer 36 remains on the annular ring 32 and slits 34.
As one could readily see, if the width of the middle part of the slit 34 is A (e.g., 0.8 mm) the polymer 36 deposits serve to reduce the width of the opening to something less than A, which then hinders the remaining non-reacted gases in the process chamber 10 from being discharged to the vacuum chamber 24.
The remaining non-reacted gases in the process chamber 10 changes the degree of vacuum in the process chamber 10. Accordingly, the degree of vacuum as indicated by the vacuum indicator 26 and the degree of vacuum in the process chamber 10 are different.
For example, if initially about 35 mTorr of vacuum is formed inside the process chamber 10 and the vacuum chamber 24, as the etching process proceeds the degree of vacuum in the process chamber 10 increases to above 35 mTorr due to the polymer 36 by-products generated and attached to the annular ring 32 and slits 34, while the vacuum indicator 26 senses the vacuum in the vacuum chamber 24 as 35 mTorr. As shown in FIG. 4, the etch rate is inversely proportional to the length of the etching process time due to the changes in the degree of vacuum in the process chamber 10, that is, the etch rate is decreased.
In particular, during an etching process to form contact holes in an oxide film (SiO.sub.2 film) on a semiconductor substrate using CHF.sub.3 as the main reaction gas, and CO as the supplementary gas, polymer 36 by-products are rapidly generated which thereafter adhere to the surface of the annular ring 32 and slits 34. More specifically, the CHF.sub.3 supplied as the main reaction gas is dissociated in the plasma state into CHF.sub.2 +F* (* : radical), that is, the active radical F* reacts with an etched layer, SiO.sub.2, forming Si.sub.x F.sub.y and O.sub.2. The O.sub.2 then reacts with the CO supplied as the supplementary gas, thereby generating the polymer 36 by-product.
Accordingly, the degree of vacuum in the process chamber 10 changes due to the polymer 36 attached on the annular ring 32 and the slits 34, but this change, as described above, is not accurately reflected at the vacuum indicator 26, whereby the etching process is inadvertently permitted to proceed at decreased etch rate.
FIG. 5 depicts contact holes formed through a certain layer 44 on a semiconductor substrate wafer W having a gate electrode 40 and a field oxide film 43. Because of the decreased etch rate, however, the bottom 42 portion of the contact hole does not reach the wafer, or the width of the contact hole is too small to perform its intended function.
In addition, the polymer 36 adhered to the annular ring 32 and slits 34 serves as source of contaminating particles, which thereafter adhere to the wafer inside the process chamber 10 and cause process failures during the etching process.
In summary, an etching apparatus having a conventional baffle plate suffers from two main problems. One is the degree of vacuum inside the process chamber changes due to the attached polymer deposits. The other is the polymer deposits serve as a source of contaminating particles, thereby resulting in a decrease in the productivity and reliability of the semiconductor device manufacturing process.